add_css_class

Description:

public void add_css_class (string css_class)

Adds a style class to this.

After calling this function, the widgets style will match for css_class, according to CSS matching rules.

Use [method@Gtk.Widget.remove_css_class] to remove the style again.

this	a `GtkWidget`
css_class	The style class to add to this, without the leading '.' used for notation of style classes